This invention relates to a process and apparatus for sparging ground water to accomplish both the physical removal and natural biodegradation of ground water contaminants.
Due to the accidental and/or intentional release of industrial byproducts, contaminants often exist in the ground surrounding many industrial and commercial facilities, as well as waste disposal sites. Many of these contaminants filter through the soil and leak into the ground water, with the result of dangerous chemicals being dissolved and/or suspended in the water. These contaminants often render the ground water unfit, not only for consumption, but also for other uses such as agriculture. Due to the need for clean water and the environmental risks of allowing the contaminated ground water to remain, it is usually desirable to rid the ground water of the contaminants.
A variety of techniques have been used for removal of the contaminants both from the soil and from the ground water. For example, U.S. Pat. No. 4,323,122, proposes the application of a vacuum to a borehole at the level of the water table, the premise being that contaminants, such as gasoline, which have a lesser density than water would stay on the surface of the ground water and could easily be removed. Because it only clears the contaminants that remain on the surface of the ground water, this procedure fails to rid the water of contaminants which are either dissolved in or suspended in the water.
Other proposals have suggested venting the soil to cause vaporization of the contaminants in the soil, and then applying a vacuum to remove the vaporized contaminants. These techniques, however, failed to treat the ground water beneath the soil. Often, the ground water beneath the soil is removed in a separate phase and treated separately. Such separate treatment increases both the time and expense necessary to treat the ground water since the water would have to be removed from the ground, treated, and then returned to the ground.
Recently, several patents have been granted on methods for treating the ground water as the soil is treated. U.S. Pat. No. 5,082,053 reveals an arrangement for cleaning contaminated ground water, which includes a pump and multiple filters placed within a pipe and located beneath the ground water level. As the water circulates through the pump, the filters clean at least some of the suspended contaminants out of the ground water. The disadvantages of this device are that 1) it requires a well shaft of sufficient diameter to house the pump and filters, and 2) the filters would presumably need to be replaced with greater frequency, the greater the concentration of the contaminants.
Another technique is shown in U.S. Pat. No. 5,076,360 and U.S. Pat. No. 5,050,676. These patents reveal methods and apparatus for vacuum extraction of contaminants from the ground involving withdrawal of liquid and gaseous phases as a common stream, separation of the liquid and gases, and separate treatment of each to produce a clean effluent. Each of these patents teaches the advantages of creating a vacuum within the well to pull up water which can then be used to flush the nearby soil. In the '360 patent, a pipe is added which releases compressed air to raise the water level and to strip the water of volatile contaminants.
The major disadvantages with these techniques is the complexity and expense which they require to clean the ground water. Both the '360 and '676 patent require a vacuum pressure to be maintained within the well. This seemingly requires the well to have an airtight casing, which may or may not be practical. Additionally, the well must be capped in such a way as to allow for a vacuum to be attached. Further, the negative pressure created within the well limits the amount of oxygen or other gasses that can flow into the ground water and promote microbial biodegradation of the contaminants by fungi and bacteria.